This thesis is written in the field of Teaching English as a Second Language, which in Norway is also known as English subject didactics. It investigates how teachers teach and readers read when developing reading comprehension in English in Norwegian upper secondary school – in general and vocational programmes. This article-based thesis comprises three articles, and uses a mixed methods approach to study qualitative and quantitative aspects of developing reading comprehension. Article I investigated 21 teachers’ reading instruction during a 4-week teacher professional development (TPD) course. The findings suggest a more active teaching of reading strategies than indicated by prior research – more active than the teachers themselves articulated. Article II showed how five of these teachers taught reading in English one year after the TPD course, how 64 of their students used the strategies offered, and how both teachers and students reflected on their strategy use. The findings indicate a clear difference between the general and the vocational programmes. While the vocational students revealed that using reading strategies made them better readers and better workers, the students in general programmes revealed that they used the strategies to meet task and teacher demand only. Article III analysed 10,331 students’ reading proficiency across Norwegian L1 and English L2. The findings showed that reading proficiency in the L2 was statistically related to reading proficiency in the L1, and to study programme. It also showed that girls read better than boys, that students in general programmes read better than vocational students, and that the majority of the poor readers are boys in the vocational programmes. In sum, the findings show that reading strategies can be valuable learning tools that help readers develop their comprehension, and that the teachers do indeed teach such strategies. The findings also suggest little reason to claim that reading strategies are effective when taught in isolation. Instead, they have to be explicitly taught by the teachers, and used independently by the students seeing personal purposes to do so. Interestingly, the most active strategic readers were indeed the less proficient readers in vocational programmes.